This invention relates to an anti-skid device for use in a vehicle hydraulic braking system, and more particularly relates to an anti-skid device that includes a damping valve for retaining and releasing hydraulic pressure in the anti-skid device.
One example of this type of anti-skid device for use in a vehicle is disclosed in U.S. patent application Ser. No. 847,779 filed on Apr. 3, 1986 which was assigned to the same entity as the assignee of the present application. The anti-skid device of that type mainly consists of three means, namely, lock detecting means for detecting the fact that a wheel of a vehicle on which the anti-skid device is installed is locked, hydraulic pressure control means for retaining the hydraulic pressure in the device when the wheel is unlocked and for releasing the hydraulic pressure in the device when the wheel is locked, thereby to reduce hydraulic pressure in a brake cylinder applying braking force to the wheel so that the wheel-lock may be released, and pumping means for increasing the hydraulic pressure in the device to bring the braking force back up to the level subsisting before it was decreased in anti-skid operation. The anti-skid device is usually disposed midway along a passage through which hydraulic pressure generated in a master cylinder by operation of a brake pedal is adapted to be transmitted to the brake cylinder. The hydraulic pressure control means is provided with a damping valve that is actuated in response to the detection of wheel-lock by the lock detecting means to interrupt the supply of hydraulic pressure from the master cylinder to the brake cylinder and to further reduce the pressure in the brake cylinder so that the wheel-lock may be released.
The damping valve aforementioned is provided with a plunger that is axially movably supported at one end thereof by a diaphragm which is mounted such as to prevent leaking of brake oil from the valve to the outside thereof. The plunger includes a cone-shaped portion formed at the other end thereof which is adapted to contact with and separate from a seat of the valve to connect and interrupt communication between a cylinder chamber of the hydraulic pressure control means and an oil reservoir of the master cylinder.
With this damping valve, however, the fastening force by which the plunger is secured to the diaphragm is influenced by the resilience of the diaphragm. Therefore, when the material of the diaphragm deteriorates owing to repeated anti-skid operations, slight clearance will be generated between the plunger and the diaphragm which results in liquid leakage. Further, in order to ensure that the valve seat is closed without fail, the cone-shaped portion of the plunger must be formed with high precision and the diaphragm also needs to be mounted very precisely so that the plunger can be displaced up and down in coaxial relation with the valve seat.